Electric fuse and setting apparatus



N. B. WALES JR ELECTRIC FUSE AND SETTING APPARATUS 6 Sheets-Sheet 1 Filed Aug. 6, 1941 SETTER -4 ATTO R N ry 23, N. B. WALES, JR 25,404,553-

ELECTRIC FUSE AND SETTI-NG APPARATUS Filed.Aug. 6,. 1941 6-Sheets-Shee-i 2 ATTORNEYS y 1946. N; B. WALES, JR 2,404,553

' ELECTRIC FUSE AND SETTING APPARATUS Filed Aug. 6, 1941 6 Sheets- Sheet 3 ATTORNEYS Juiy 23, 14.

N. B. WALES, JR I 2,404,553 ELECTRIC FUSE AND SETTING APPARATUS Filed Aug. 6, 1941 e sneefis-she'et 5 I BBC ARMED INERT INVE ,R'

. ATTQRNEYs Juiy 23, 1946. N. B. WALES, JR 2,404,553

ELECTRIC FUSE AND SETTING APPARATUS e Sheets- Sheet s Filed Aug. 6,- 1941 ATTORNEY$ E MP Patented July 23, 1946 2,404,553 V ELECTRIC FUSE AND sarrmo APPARATUS Nathaniel B. Wales, Jr., New York, N. Y.

Application August 6, 1941, Serial-No. 405,570"

9 Claims. (Cl. 10270.2),

This invention relates to electric timing systems and methods adapted to set and initiate the operation of ordnance devices, such as explosive shells, submarine depth. charges, aircraft bombs, flares and the like, at a predetermined time measured from the instant of firing or release thereof.

Heretofore, time fuses which have been employed in practice for similar purposes have been largely limited either to pyrotechnic fuses or to mechanisms of a purely mechanical nature, similar to a type of clockwork with a controllable escapement. Although electrical time fuses have previously been proposed, they have been subject to many disadvantages which are overcome by the present invention.

The time fuses and fusesetting apparatus in accordance with the present invention include a large number of advantages among which may be mentioned compactness which is of particular importance in shell fuses, accuracy of timing regardless of weather conditions, simplicity of fuse parts, rapidity and economy in manufacture, and safety in use. The construction according to the invention also allows of thorough testing of the fuses under the same conditions as in actual use.

The fusesetting apparatus in accordance with the present invention makes possible the setting of each time fuse immediately, before it is released with its projectile. This enables the setting of each time fuse individually before it is fired or released, whether it be on the ground or in an aircraft, for example, thus introducing great flexibility in the control of the timing of detonation, with many resulting advantages which heretofore have been impossible of attainment, especially in warfare. The mentioned flexibility of control includes the ability to set simultaneously while in flight all of the bombs in an aircraft, if they are to be dropped on the same target; and in the event of emergency, the ability to instantly render the timing circuits of all Of the bombs inert to make possible jettisoning the bombs without detonation. Furthermore, the fusesetting apparatus of this invention allows of a considerable range of control of the time periods to which the fuses may be set and also includes provisions assuring readiness and accuracy of the settings, and the entire equipment may be self-contained and portable.

Many of the advantages above mentioned, as well as others which will appear hereinafter, result from the fact that my invention introduces the functional separation of the component elements of the timing circuit from those of the ignitioncircuit in the fuse so that each element of those circuits may be chosen for optimum per: formance in its location. Not only is it thus possible to choose the circuit-elements specifically for their intended functions, .but from thisrresults simplification of the entire 'mechanism, greatly improved reliability and reduction of the physical'size and of the cost of manufacture. To illustrate: the timing circuit of the fuse must employ accurate component parts, but little'actual electrical energy is required purely for tim-. ing, whereas the ignition circuit should include ample electrical energy to assureignition, but as long as it is sufficient the exact quantity of ignition energy is not important.v Therefore, by means of this separation of elementsI am able to use in the timing circuit of the fuse accurate timing condensers, preferably of the paper wound type, and small both in'size'and capacity,

and in the ignition circuit a high-capacity condenser which need not'be especially accurate but interval, the discharge in the ignition circuitis controlled by relay action initiated-in the timing circuit. In accordance with the preferredform of my invention this relay action may be performed by a gaseous discharge tube of the three-electrode type, and thus the invention comprises an electronic time fuse. H

As an example of the great improvementsin compactness introduced by the fuse of thisinvention, it may be mentioned that only twocondensers of sufficiently large electrostatic capacity to furnish detonating energy at reasonable voltages would, if they also must be of an accurate type to be used fortiming purposes, oc-j cupy a volume about four times as great as the volume occupied by three condensers according to the present invention.

By combining certain electrical and mechanical features in the design of the fuse of this invention an unusually large number .of safety devices have been made possible, some of which 7 are interdependent whereby the possibility of accidental detonation is further prevented. I

By employing low levels of energy in'the timing circuit it is possible not only to improve the structure and operation of the fuse, but it .is likewise possible to simplify the structure and improve the operation of the fusesetting apparatus, because the required setting voltage may then be lower than would be required for timing condensers previously proposed.

Many additional features and advantages of the present invention will appear from the following description which is to be read in connection with the drawings, wherein:

Figure 1 is a circuit diagram of a complete time fuse system in accordance with my invention, including timing apparatus and setting apparatus therefor, and which is especially adapted for use with time fuses for shells;

Fig. 2 is a circuit diagram of an alternative embodiment of the timing apparatus for shell fuses;

Fig. 3 is a view in vertical section taken through a shell fuse incorporating many of the features of the present invention;

Fig. 4 is a horizontal section through the line 4'.4 of Fi 3;

Fig. 5 is a horizontal section through the line 5-5 of Fig. 3;

Fig. 6 is a circuit diagram of a time fuse and setting apparatus therefor, particularly adapted for use with aircraft bombs and flares, or submarine depth charges;

Fig. 7 is a graphical representation of the charging voltages required to effect a certain preselected range of delay in the time of detonation of one example of the fuse circuit of Fig. 6;

Fig. 8 is a View in vertical cross-section of a time fuse constructed in accordance with my invention and adapted for use in connection with aircraft flares, bombs and the like;

Fig. 9 is a horizontal section through the COlllposite plane 8-8 of Fig. 8;

Fig. 10 illustrates in broken section a combination charging plug ejector and isolation switch structure applicable as a modification to the structure of Fig. 8

Fig. 11 is a view in partial cross section of a modified form of the ejector and switching device of Fig. 10, together with additional safety mechanism suitable for an aircraft bomb or flare;

Fig. 12 shows in side elevation the mechanism of Fig. 11 in a position in which it would be released from an aircraft;

Fig. 13 is a circuit diagram of a preferred embodiment of my invention as applied to aircraft fuse and fuse-setting apparatus;

Fig. 14 illustrates graphically the time intervals as a function of impressed fuse voltages, for

the several ranges of detonation time available in a certain embodiment of the system shown 1n An understanding of the timing system in accordance with my invention may be had by reference to Fig. 1 of the drawings, which is a circuit diagram of one modification thereof as applied to the time fuse for a projectile such as a shell. In this circuit diagram is shown also a suitable fusesetting apparatus or circuit by which the timing circuits may be set to operate after a predetermined delay or time interval.

In Fig. 1 the timing circuit proper is shown as comprising condensers Cl and C2 connected at the bottom to a common terminal which combe the same, depending on the requirements. These condensers C1 and C2 may be of the paper wound type and be of small but accurate rated capacities. One terminal of resistor R1 is connected to the contact d and the other terminal is connected to the control electrode or grid G of the gaseous discharge tube I.

The output or controlled circuit of tube I includes in series an ignition condenser C3 and a resitsance 44 which in this embodiment comprises the element to be controlled, viz: a detonator resistance or ignitor. One terminal of ignition condenser C3 is connected to the common terminal E0 and also to the cathode K of tube I, and the other terminal of condenser C3 is connected to the pole of switch 2| which moves to make connection with the contacts 0 and (1 according to whether that condenser is to be placed in a charge or discharge position. This ignition condenser C3 may conveniently be of the electrolytic type which ha a large capacity and is much cheaper in high capacity sizes than a paper type condenser. Being merely a source of igition voltage the magnitude of its electrostatic capacity is not critical. In the embodiment here being described this condenser was of 8 microfarads.

The operation of this timing circuit is as follows: Assuming switches and 2| to be moved to the left to make connection with contacts 0 and that appropriate potentials are applied at terminals E1, E0 and E2, respectively, condensers C1 and C3 will be charged with corresponding potentials. Then if condensers C1 an C3 be thereafter connected to the discharge contacts 01 by movements of switches 20, 2|, the charge in ignition condenser C3 will continue to be stored therein because of the normally nonconductive condition of the discharge path of discharge tube I between plate P and cathode K. However, as soon as connection between switch 20 and contact d is made, condenser C2 which may be assumed to have had no initial charge will begin to receive a charge from the potential of C1 which will discharge through timing resistance R1. As the charge in condenser C2 increases, a rising potential is applied between the control electrode G and cathode K of tube I. This process continues at an exponentially decreasing rate determined by the magnitude of the resistance R1 and the initial charges in condensers C1 and C2 until the potential across G and K increases to the breakdown potential of the gas-discharge path between those electrodes. As a typical example, this potential might be between and 100 volts. When this potential is reached discharge occurs between G and K and the entire discharge path of the tube becomes ionized, and the effective resistance of the path between the plate P and cathode K is greatly decreased. This decrease in resistance of the discharge path a1- ows the charge stored in condenser C3 to be discharged through resistance 44 which then becomes heated and effects the ignition or detona- 7 tion desired. The electrical charge stored in the ignition condenser should preferably be in excess of that required to effect ignition.

From the foregoing description it will be observed that gaseous discharge tube l is in eifect a relay, the discharge path between G and K being the control or input side and the discharge path between P and K being the controlled or output side. Thus, the discharge path of the relay tube operates effectively to couple the timing and ignition circuits, these circuits otherwise being electrically isolated from each other. The term electrically isolated is not used here nor in the appended claims to indicate that the ignition and timing circuits are electrically insulated from each other, but only that the ignition circuit is controlled by the timing circuit solely through the discharge path within the tube, and. that in all other respects the timing and ignition circuits, and the elements thereof, are functionally independent of each other. Because this tube operates in response to an electrical impulse from the timing circuit to release the ignition energy its operation may be referred to as a trigger action. The use of such a relay introduces not only the economies of space and expense, but also has been found greatly to increase the accuracy of timing and the raliability of operation of the entire system in the manner previously pointed out.

Suitable timing circuit setting apparatus is represented at the left of the charging terminals E1, E and E2, and may include any convenient source of direct current of sufficiently high voltage, an appropriate device for maintaining the output voltage constant under varying loads, and a control device whereby the charge stored in the timing circuit condenser may be adjusted in order to set the timing circuit for the desired time interval. The apparatus as here shown comprises a battery 52, such as a storage battery, and a control switch 53 in circuit with a motor generator ll-5l. Generator 5| can be designed to have a higher voltage output thancould conveniently be obtained from a storage battery, for example. Any other suitable source of direct current at the required potential could of course be substituted; for instance, if alternating current were available a rectifier and filter could be employed. In the illustrated system a gaseous discharge type of voltage regulator tube T1 is shown for maintaining more nearly constant the working voltage of this voltage supply.

A bleeder or potentiometer R3 is provided with a fixed tap 60 and an adjustable sliding contact indicated by the arrow. Thus the voltage as impressed across charging condensers Cr and C5 will represent an adjustable voltage E1 and a fixed voltage E2, respectively, in reference to the common return or zero potential E0. This charging system thus allows the calibration of potentiometer R3 in terms of time intervals, such as seconds.

It is contemplated that the three contact points E1, E0, E2 may be connected by any suitable conductive means, such as a multi-wire cable or charging harness to three contacting areas or charging electrodes on the surface of the fuse body, such for example as those shown on the surface of the shell fuse illustrated in Fig. 3, namely, 9, II and [6-H respectively. For the rapid setting of shell fuses a suitable box or receptacle may be arranged to include charging contacts so spaced that they will connect with the corresponding charging electrodes on the surface of the shell. Thus before a given shell is fixed it may be quickly inserted in such a charging receptacle and almost immediately withdrawn with the assurance that the timing and ignition condensers will have received the charges predetermined to effect detonation after the desired delay timed from the firing. A preferred embodiment of such a charging receptacle provides for charging the fuses of shells as they are loaded into the breach of a gun. It may comprise an ar-.- rangement of charging contact fingers secured to or near the breach'mechanism soas to allow the shell to pass through the contacts in a continuous motion as it is moved toward or intothe breach. Thus, in rapid fire operations, the timing of the fuses may be changed very rapidly and, immediately before each shell is fired. J

Switches 20 and 2| together with the electromagnet coil l5 represent an electro-mechanical relay which will be described in detail in connection with Fig. 3. It will here sufiice to state that switches 20 and 2| normally remain in the neutral or unconnected position shown in Fig. 1, but when a charging potential is impressed across contact points Eo-E2 the electromagnet I5 actu ates the relay and moves switches 20 andll to connect with the charging contacts 0, thusallowing condensers C1 and C3 to be charged. After a very brief interval the'charge will have been stored in these condensers and the charging voltages may be removed, whereupon switches 20,- 2i return to the neutral position shown. In this position the charges will be accurately retained and a minimum of leakage will occur even though the exterior ofthe shell be immersed in water; Thereafter when the shell is fired switches 20, 2| are automatically moved by inertia'to make con nection'wi'th discharge contacts d whereupon the timing operation will commence and proceed 'as above describeduntil detonation occurs.v "1

Fig. 2 is an alternative modification of the fuse system shown in Fig. 1 and is in general sim: ilar thereto except that a four-pole switching re-'- lay, including coil l5 and switch arm Eli, 51, 58 and 59, is employed in place of the two pole switch shown in Fig. 1. J

In operation the circuit arrangement-of Fig. 2 differs from that of Fig. 1 in that both condensers C1 and C2 are charged to the same pro-selected potential when the switch poles are thrown to the charging position 0. In this position the ignition storage condenser C3 is charged through switch pole-s 58, 59 to a potential in itself capable of efiecting the necessary ignition of resistance 44 but incapable of discharging through the highresistance discharge'path P-K" of gaseous discharge tube l. However, when .the shell is fired, i. e., on setback, the switches are thrown to the discharg position 12 thus connecting condensers C1 and C2 in series across electrodes G and K of tube l, but with such polarities that the charges oppose each other and thus resulting in an absence of potential difference across these two electrodes due to the initial equality and opposition of their potentials. For this reason the discharge path will not be triggered or ionized until condenser C2 has discharged itself sufl'lciently through high resistance R1 as to produce'a difference of potential between C1 and C2 'sufficient to'initiate the required trigger discharge between electrodes G and K. Condenser C1 will discharge very lowly because there is connected across it the high resistance R1 in series with the still higher.'resistance of the non-conductive discharge path G-K. When this dischargeoccurs the relay ac tion as described in connection with Fig. 4 results and the ignition charge stored in condenser C3 will be discharged through detonator ignitor 44.

The structure illustrated in Fig. 3 represents an elevational view in section of a shell fuse which includes many features of the invention, although the construction is equally well adapted to a timing fuse for use in connection with any type of projectile which would inpractice be sub,-

7 iected to a reasonably high initial or discharge velocity.

The shell fuse body of Fig. 3 is as a whole, as shown, composed of two separable assemblies. The upper of these assemblies consists of the annular metal block I6 and its associated parts, while the lower assembly consists of the metallic casing I'I, together with the components held within or secured to it. Upper block I6 forms with metallic plates 41 a chamber retaining an electromagnetic field winding I5. The magnetic circuit of this winding includes magnetically permeable elements including block I6, plate 4? and the cylindrical armature slug I4 which is centrally guided and axially free to move within a non-magnetic guiding sleeve 45. Screw I9 secures to the lower extremity of the armature slug I4, an insulating washer I8 carrying a peripheral groove 26. In this groove are carried spring switch leaves and 2!. These switch leaves when moved upwardly make contact, respectively, with the upper or charge contacts 24 and 23, and when moved to the downward position make contact, respectively, with the discharge contacts and 24. Switch leaves 23 and 21%, as well as the contact leaves or strips which carry contacts 23 and 2d are shown more clearly in Fig. 5. Contact strips 22 and 25 are arranged similarly on the opposite side of switch leaves 2i and 20. In the drawings the same reference characters have been used for the switch contact leaves and for the contacts carried thereon. As many contact leaves and contacts as required may, of course, be employed.

All of the contact and switch leaves are spaced and insulated from each other by spacing insulation 36 and 37 and insulating gaskets 35 and 38. Six screw 2! symmetrically spaced secure the upper assembly parts into a unitary structure. Insulating and spacing members 35, 36 and 38 centralize and insulate screws 2'! from contact with leaves 26 to 25, inclusive.

The upper extremity of armature slug I4 is formed to include a cam-shaped head i! which cooperates with two sp g pins 12 to form looking means for the armature and the switch leaves. As shown in Fig. 4 these pins pass diametrically through the entire upper fuse assembly in such manner that they may be inserted from the outside after the upper assembly has been completed and tested. Pins I2 normally limit the motion of the armature slug M- against downward motion from its central position, as illustrated, due to the conical shoulder on the head iI. Armature AI may move upwardly a distance equal to the length of the post shown just below the head 4i. However, when the projectile which carries the described fuse is given an initial acceleration due to firing, as from a gun, the force of inertia on slug I4 will tend to spread apart spring pins I2 by reason of the cam action of head ll, and the slug will move downwardly to a limiting position defined by the backing plate 39.

Included in the lower assembly is a cylindrical lower casing I'i which, for example, may be made of aluminum and formed to include several cavities. The upper cavity 29 is shaped to accommodate, in a preferred embodiment of the invention, two timing condensers which are designated in the circuit diagrams of Figs. 1, 2, 6 and 13 by reference characters C1 and C2. These timing condensers may preferably be of the impregnated paper wound variety, and in any event should be of a high grade and accurate type but small in dimensions. The cavity is formed to include an ignition energy storage condenserwhich may preferably be of the electrolytic type, and in any event need not be of especial accuracy in rated capacitance, although it should be large enough to store a charge more than normally required to efiect ignition. These condensers may be retained in their respective'cavities in any suitable manner, such as by a sealing compound. .Insulated terminal lugs '28 serve as electrical tiepoints to interconnect the upper and lower assemblies in the stages of manufacture, after which the lower and upper assemblies may be secured together by set screws 54.

Cup 34 of suitable material which may be screwed into casing I'I contains a detonating compound such as black powder, in Which is imbedded an ignition filament wire 44. The detonating leads 42 and 43 are connected to the ignition wire terminals 45 and are suitably insulated, as shown, where they pass through the walls of cup 34. Conduit holes 3| serve to carry leads 32 and 43 up to the terminal tie-points 28. In projectiles requiring accurate dynamic balance, duplicate holes 3| may be formed in the opposite side of the casing. The lower extremity of casing I'I carries, as shown, an external base thread 32 which may engage a shell forging, and an vinternal thread 33 which may be utilized to engage a booster cup which usually includes a powder charge, a centrifugal safety gate and other elements of the usual ordnance shell.

The upper assembly of the fuse includes a relay in the form of a gaseous discharge tube I which is seated on an annular hard rubber cushion I3 within the cylindrical cavity of an insulating form ii which may be of Bakelite, for example. Between insulating form 8 and the wall of tube I a sleeve or tube 6 of suitable material such as fiber may be interposed. A rubber cushioning cap I serves to complete the protection of relay tube I by pressing it resiliently against the cushion I3.

Within tube i are included, in the device illustrated, three electrodes of tungsten or other suitable metal, two of whichmay be in the form of rods, comprising the anode or plate 2 and the grid or control anode 3. These electrodes should be spaced closer together than any other pair in order that the break-downv potential between them be much less than between any other pair. A semi-cylindrical and coated conductive sheet '4 with its support 5 constitute the cathode of this relay or gaseous discharge tube. This relay is represented in the schematic circuit diagrams of Figs. 1, 2, 6 and 13 by reference numeral I and the three electrodes 2, 3 and 4 thereof as P,'G and K, respectively. The envelope of relay tube I encloses the electrodes in a gaseous atmosphere which may comprise an inert gas such as helium, argon, nitrogen, mercury vapor or a suitable mixture thereof. While the drawing of Fig.3 is not exactly to scale, it, together with Fig. 4, illustrates the order of magnitude of curvatures of the electrodes which have been determined after extensive experiment to meet the unusual requirements of such a relay for the described purpose. The various engineering requirements involved in the design of such a tube include consideration of the ignition voltage, pre-ignition current, cathode current density and differential field gradient necessary for correct operation at a given gas pressure. Also, the stress requirements of initial acceleration of the order of 1500 grav it-ies as well as extreme compactness must enter into the design for a tube to be used in highvelocity shells. For low velocity purposes, "as in the case of Fig. 8, the design is not so critical, and commercially available tubes may be employed. Furthermore, the more lenient requirements of fuses in which setback is absent would alternatively permit the use of an electrochemical type of relay adapted to trigger at a predetermined control current in place of the equivalent gaseous discharge relay.

Metal cap 9 secured to insulating form 8 by screw I9 completes the entire assembly which presents three external metal surfaces, 9, II and I6l1, insulated and spaced from each other and which form three external electrodes through which charging potentials may pass, when such contact electrodes are placed in suitable conlnection with corresponding charging contacts arranged to cooperate therewith, as described in connection with Fig. 1.

The mechanical operation of the fuse structure illustrated in Figs. 3, 4 and is as follows: When a suitable electric current is passed through field winding l5 the resulting magnetic flux tends to draw armature slug It upward toward the head of the fuse until it subtends the greatest flux density. This motion displaces the spring switch leaves 28 and 25 away from their normal central position as shown. In the normal or central position the switch leaves do not make connection with any other contacts. This magnetically actuated motion of leaves 20 and 2| brings them into connection with the upper fixed contacts 24 and 23, respectively, and this connection is maintained only so long as the actuating current passes through the field coils l5. The time of this contact may be called the charging time and during this period the electrical connections are those of Figs. 1 and 2 when the switches 58 to 59, inclusive, are in the charging position indicated by the contacts designated 0. At this time the potentials necessary to charge the timing condenser Ci of Fig. 1, and condensers C1 and C2 of Fig. 2, and the ignition condensers C3 of both figures are applied to those condensers through suitable connections to electrodes 9, II and l6-ll on the surface of the fuse. When the charging is completed and the flow of this actuating current is stopped, contact springs 20 and 2| will return to their normal position, as shown. In this position the external contacts or electrodes 9, II and IB-l'l are completely disconnected from the circuits of the fuse, whereby the charges stored in the condensers will be unaffected by surface moisture or other conditions which might tend to shortcircuit the external electrodes, and the accuracy of the timing will be assured.

Spring pins l2 normally limit the motion of the armature slug it against downward movement from its normal central position shown, due to the conical shoulder on the lower portion of the head 4i. However, when the shell is subjected to setback in the initial acceleration resulting through its discharge, as from a gun, the force of inertia on slug i l will urge apart the spring pins 12 by cam action, and the slug will move downward as previously described to a position limited by the backing plate as. This motion carries spring switch leaves 29 and 2| into connection with lower fixed contacts 25 and 22, respectively. Furthermore, the contacts will be locked in this position even after the setback acceleration has ceased because the upper contour of head il after passing spring pins 12 is unable to spread pins l2 by reason of the fact that the spring pressure thereof is V 10 greater than the spring pressure of the Contact leaves 20 and 2|. 7 s

As soon as contacts 20, 25 and 2 l, 22 are closed the timing action of" the fuse is set into opera: tion. The circuit connections may then be il-f lustrated by Fig. 1 or Fig. 2 under the conditions when switches 54 to 59, inclusive, are in the discharge position represented by contacts marked d. Thus when the timing circuits'are connected in this discharge position the cletonaktihg'dg: vice will be actuated at theexpiration'of the time represented by the predeterminedcharge stored in the timing condensers as' described previously in connection with Figs. 1 and '2 An important advantage of this invention resides in that it makes possible the complete test-1 ing of all the operating portions of" the fuse under normal operating conditions. This re sults from the fact that the weighto-f 'slugM' is such that when thefuse is stood upright; the

spring-tension, if any, of the switch 'leaves' ;is

overcome, and contacts 22, 25 close, providing of course that spring pins It have not been in serted. Thus, before pins it are inserted,"both the timing and the ignition circuits and the relay l5 may readily be tested.

The system illustrated schematically'in Figfi represents a complete time fuse and fusesetting apparatus which broadly speaking is similar to that of Fig. 1. Howevergthe system of Fig.5 is different in certain respects and includes ad, vantages additional to those :of Fig. 1.. The

system of Fig. 6 is adaptedmoreparticularlyto I the requirements for time fuses and setting ,aps'

paratus for aircraft bombs'andjflares which it is desired to ignite at'a predetermined. time aftertheir release from the aircraft; 'It is' usu-" ally desirable to initiatethe timing automatically at the instant of separation of the bomb .01 flare and its fuse from the fusesetting apparatus in; stalled in the aircraft. This characteristic is, also desirable in a fusedesigned for anti-sub-i marine depth (:harges'wherethe desired depth for detonation is predetermined in terms of 'its' time rate of sinking. 7

As indicated previously herein an unusual advantage of the presentinvention resides inlthe fact that itmakes. possible the setting of each timeffuse individually the instant before itis released from the. aircraft. This enablesthe detonation of the bomb or flaretoibe jeifected at any desired altitude or at theexpiration of any desired time interval after release from the aircraft regardless of the altitude of the aircraft itself at the time ofv release. In previously known time fuses for aircraft use it has been neces-' sary to estimatein advance the probable alti tude of the aircraft at the time of releaseof all of the bombs or flares because it was necessary to set the timing of the fuses before the bombs or flares were loaded in the aircraft. 'Once the flares or bombs had thus been loaded in the aircraft it was impossible thereafter to change the setting of the timing mechanismvrithout first landing the aircraft, a 7 v} Q In connection 'withthe systemof Fig. 6v (and with Fig. 13)' it is to be understood that an'appropriate charging cable harness will be employed to connect the fusesetting apparatus with the several bombs or flares stored in the bomb bay of the aircraft. Generally speaking, requires merely the necessary connecting-"wires grouped into a cable running from the terminals it-13 inclusive of Fig. 6 and'dividedinto as ma y electrically parallel branches as there are fuses 11 to be set. ,At the terminal of each branch is an appropriate charging plug which 'is placed in electrical contact with the charge electrodes of each individual fuse. Such plugs are described in more detail in connection with the fuse strucl es illustrated in Figs. 8 to 12.

Referring now to Fig. 6. above terminals 1043 are shown the circuit connections of a fusesetting apparatus suitable for use in aircraft and which in itself may be compact and rapidly adjusted to set the fuses connected thereto individually for any desired time delay of detonation. This setting apparatus is adjustable by means of a multiple switch shaft 62 having a plurality of positions arranged to subdivide the setting voltages, corresponding to the total range of time intervals over which the fuse is operable, into a number of contiguous scale-ranges. A pointer or knob Bl indicates the scale-range in operation. ;In the drawing, three such scale-ranges are illustrated and labeled A, B and 0 respectively, and these cover the decade time intervals of ,10-20, 20-30, and 30-40 seconds, respectively. The poles S2 and S3 of switch 62 are connected so as to progressively subtend three adjacent intervals of voltage across a bleeder resistance comprising resistors R8, R9, R and R11. The potentials along this bleeder are sustained by current source 69, here represented as a battery but which may comprise any suitable source of direct current as explained in connection with Fig. 4. This current source has three progressively higher potential taps E4, E5 and E6. A potentiometer R3 is connected across switch poles S2 and S3 and the adjustable slider on this potentiometer is connected as shown through charging contact H to charging electrode E1 of the fuse. Thus there are three adjacent ranges of voltage which can be delivered to the fuse,

these ranges being selectable by the switches S2 40 and S3, and within each range the Voltage may be subdivided by potentiometer R Switch S5 is provided. to conserve the current when the fusesetter is not in use.

The movement of a voltmeter 68 is connected 4.)

so as ,to indicate the subdivision of the interval which the adjustable tab of potentiometer R3 subtends. CQnseqllently, a full scale deflection of this meter movement may be produced by the voltage available in each range, providing the series multiplier resistance connected in circuit with themeter is selected to yield full scale deflection for the total voltage in each interval. This selection of correct meter multiplier resistance is effected by switch pole S1 which successivelyintroduces multiplie resistances R5, R6 and R7 automatically with the turning of shaft 62 by manual selector knob 6|.

Provision is made to check the total voltage across the bleeder by displacement of switch S4 0 10 fuse in terms of time.

to the alternative position from that illustrated.

The resulting connection introduces meter multiplier R13 in circuit with the meter so that full scale meter deflection then corresponds to the peak voltage across the bleeder. The series regulation rheostat R12 allows adjustment of the bleeder "voltage to a predetermined operating value.

As a convenience in reading the meter separate scales 64, and 66, each subdivided in 1-0 graduations of one second each, may be carried on a plurality of cylindrically polygonal faces so phased with the range positions of shaft 62 that only the corresponding scale presents itself on the face of the instrument at any given setting system above described provides an adjustable voltage E1 to the charging cable harness connection 1 l, a fixed voltage IE2 at connection 1.3 for charging the ignition storage condenser Q3 of the fuse, and a zero or ground return E0 at connection if. A fourth connection 10 is provided which is connected by a jumper in the charging cable plug to the zero potential lead 12.

The circuit arrangement and circuit elements of the time fuse apparatus are similar to that of Fig. 1 except for certain improvements now to be described. The components of the fuse comprise as before, preferably timing condensers C1 and C2 of the accurate paper-insulated variety, an ignition energy storage condenser C3 preferably of the electrolytic type, a detonator or igni tion wire A l, gaseous discharge tube I, ahighresistance leakage resistor R1 and a-limiting resistor of medium resistance value R2 later to be described. The timing condensers may be of 0.5 microfarad and the ignition condenser of about 20 microfarads capacity. A structure suitable for such a fuse circuit, together with a charging plug therefor, is described in connection with Figs. 8 to 12 inclusive.

The operation of the fuse represented in Fig. 6 is similar to that of the fuse represented in Fig. 1, it being recalled that the fuse of Fig. 1 is especiall-y adapted for use in connection with a shell of comparatively high velocity whereas that of Fig. 6 is more especially adapted for-use in connection with missiles of low velocity such as aircraft bombs and flares.

During the time when the fuse of Fig. 6 is connected to the setting contacts 18-13 the condenser C2 is shortcircuited by a shortcircuiting connection or jumper between contacts Hand 12. This jumper may be included in the wiring of a suitable charging harness which would interconnect the fusesetting apparatus and the several fuses as already described. While condenser G2 is shortcircuited no voltage is impressed across electrodes GK of tube l and no discharge of that tube can occur. However, due to thelarge value of timing resistance R1 this external shortcircuit does not prevent the adjustable tap of potentiometer R3 from maintaining a preselected voltage on timing condenser 01. Consequently when the bomb or flare containing this fuse is dropped the resultant breaking of the connections at contacts lit-l3 removes the shortcircuit from C2 and thereby initiates the exponential rise of potential in condenser 02, which comprises the 5 timing process as described in connection with Fig. Z.

The value of resistance R2 being negligible in comparison with resistance R1 the rising potential in condenser C2 will at the predetermined time reach the breakdown potential of the path between electrodes G and K of tube I. The sub- 13 niter M with the discharge of the energy stored in ignition condenser C3.

Limiting resistor R2 may be connected in series with a control electrode G to insure that the final discharge characteristic of the tube I will be identical with those measured during the test and inspection operations of manufacture. This precaution derives fhom the discovery that any discharge within the cold cathode type of tube such as tube i which exceeds certain minute values of current density will probably alter the characteristics of the tube for its next discharge. Thus without some means for compensating for such alteration of characteristics the mere testing of the circuits including such a gas discharge tube may change the characteristics thereof so that when it is thereafter employed for the intended purpose it will not operate according to the characteristics observed during the test. Furthermore, since the value of ignition potential is a function of the pre-breakdown controlelectrode current any series limiting resistor, such as must be used in manufacturing inspection to prevent alteration of the discharge potential characteristics will change the exact required voltage at which the rising potential will ignite the tube. For this reason resistor R2, which in the embodiment described Was of 10,000 ohms, is permanently incorporated in the fuse both for manufacturing tests and for final operation so that the behavior of the tube will be identical under both circumstances. Such resistor should not be incorporated in the plate electrode or ignition circuit as it would limit the detonating current. However, the discharge potentials of the plate-to-cathode (P-K) path obtained without and with such a limiting resistor in the control circuit do not differ sufliciently to be of significance, nor does the presence of this limiting resistor in any way affect the accuracy of timing because the initiation of discharge is the sole function of the control electrode due to the fact that the potential which is supplied to the ignition energy condenser C3 is intentionally inadequate to produce discharge across the discharge path PK without aid from the trigger discharge effective between electrodes G-K.

The graph illustrated in Fig. '7 represents the relation between the charging voltage (E1) stored in timing condenser C1 and the time required to trigger the discharge path G-K. of tube I in Fig. 6. This curve is of course exactly representative only of a certain time fuse circuit with certain components as employed in the measurements from which the curve of Fig. 7 is derived. However, it may be taken as generally representative of the relations which may be expected from a fuse circuit of the type described and indicates the order of magnitude of the charging voltages required to be impressed on condenser C1. This curve of Fig, 7 indicates that due to the exponential nature of the time-voltage relation, the successive decade time ranges corresponding to the positions A, B and. C of the range selector knob 6| in Fig. 6 will subtend decreasing ranges of voltage.

It is also to be noted in connection with Fig, 7 that as the slope of the curve becomes more flat the statistical mean deviations of fuse timing operations from the preselected values may be expected to increase due to the consequence that a given uncertainty, either in the ignition voltage of the tube or in the constancy of the voltage supply to the setting apparatus, will subtend an 14 increasingly larger corresponding uncertainty in the exact time of ignition.

The mechanical construction of a time fuse having various safety and control features, all in accordance with the present invention, is illustrated together with certain modifications in Figs. 7

8-12, inclusive. It is to be understood that the fuse mechanism in these figures may include, for example, the time fuse circuit illustrated in Fig. 6, or in Fig. 13. This structure, with its modifications, was originally designedas a fuse for aircraft flares and bombs, but it is also applicable to other uses, as will occur to those skilled in the art.

Referring first to Figs. 8 and 9, a cylindrical fuse body I ll is shown to be closed at its upper end by a head bushing l l 8 intowhich is threaded an arming vane switch casing 18. A base I I9 for the fuse body supports an adaptor I bearing external threads i2l provided to engage the bomb forging or flare body as the case may be. .A small propeller or air vane 14, here represented as including two vanes, is secured to bushing 15 which is journaled axially in casing 18 ,so that hearing balls 1'! receive the thrust of air pressure on vane T4. Rotation of vane 14 due'to the free fall of the bomb or flare to the nose of which it is attached rotates a driving spur gear 19 which is secured to bushing 75.

Axially threaded in the bushing 15 is a sleeve 49 which is integral with a driven gear'80. This driven gear differs by one tooth from driving spur gear 19. Pinion gear 8| engages both of gears 1'9 and and is arranged to revolve freely on a fixed axis. Thus the rotation of bushing 75 will slowly revolve screw sleeve 49 by reason of the epicyclic gear action resulting from" the gear train just described. Since this screw sleeve 59 is threaded into bushing 15, as shown, the rotation of the sleeve will progressivel move the sleeve downward. 7 V

, Secured to sleeve .49 is an insulating stud 82 to which is secured contact disk 83 and spring backs .ing washer 84. The downward motion of sleeve d9 above described will therefore progressively carry the contact disk 83 downward until, after a predetermined number of revolutions of the sleeve, contact screws 35 and 86 will be connected together by contact disk 83. Contact screws 85 and B6 are insulated from base plate 81 by washers 88. These contact screws are connected and it is to be understood that a similar switch may be inserted in the circuit of Fig. .6. It will be obvious that the motion of sleeve 49 may be made to engage any suitable switching device at the'predetermined'nuniber of vane revolutions, and that this switching operation may comprise the complete electrical disconnection or shorteircuiting, or both, of ignition device I23 (Fig.

It will be seen that when this safety or arming switch is open detonation by actuation of the ignition circuit cannot occur under any circumstances. and also that it cannot occur until, by operation of the air vane mechanism, the bomb or flare carrying this air vane has dropped a suf- 15 ficient distance to efiect electrical connection across contacts 85 and 86.

Prior to release of the fuse from the aircraft, vanes I4 are prevented from rotation by stop arm I6, secured to bushing I5, which is locked or secured to bracket 89 aifixed to the fuse body I IT. A so-called arming wire 9| locks together stop IE and bracket 89 by passing through suitable holes therein. When it is desired to release the bomb r flare from the aircraft, arming wire BI is withdrawn from the bracket and stopped, either manually, or by reason of the fact that one end of the wire 9| has been secured to the structure of the aircraft from which the fuse is dropped.

In order to prevent fouling of the charging cable harness and at the same time to provide certain switching facilities desirable to perform at the instant of release of the fuse, an ejection plunger 92 is provided to slide through bushing 93 (Fig. 8) Secured to the opposite side of the fuse body III is an insulating bushing I09 carrying suitable contacts IIlS (this bushing and contacts being formed as a receptacle) to which may be secured connecting wires such as 9'! and 98 connecting with the appropriate elements of the timing circuit. A spring 9t acting against an insulating plate 95 on plunger 58 tends to urge the plunger through the receptacle to press against charging plug IUI which terminates the charging cable I02. Spring 94 should be of sufficient strength to insure, when released, the election of charging plug I8 I As will be observed from the drawings, arming wire 9| when in position is arranged not only to lock the air vane from revolving but also to prevent ejection plunger 92 from moving in the direction of plug IBI. This result is achieved by providing holes through bushing 93 and plunger 92 through which the arming wire passes. As a consequence of this additional locking feature plunger 92 is unable to move until the instant of release of the fuse at which time the withdrawal of arming wire 9| permits plunger 92 to eject plug IBI and disconnect it from contacts I68, finally coming to rest against stop shoulder or head I60.

Secured to plunger 92 is an insulating plate 95 which therefore moves with the plunger. This late carries four (or a different number if required) spring switch leaves I26-I29 which, in the charging position prior to the ejecting action of plunger 92, connect with switch contact points I04--IflI. These contact points are secured to an insulating plate I03 which in turn is secured to the base H8 of the fuse body by suitable sup porting brackets IIB. This construction facilitates assembly of the entire structure. By combining this switch means with the charging plug ejection means an additional feature of safety and accuracy is provided by enabling the automatic changing of circuit connections at the instant the fuse is disconnected from the charging cable.

In certain fuse circuits (see Fig. 13) it is desirable, not only to break but also to make contact at the instant of release of the fuse. For this purpose a contact point 48 is provided so that the associated switch leaf functions as a single pole double-throw switch, whereas the remaining poles may be simply single-throw poles, as shown. The switch poles and corresponding contacts just described are illustrated at the lower portion of Fig. 13 in a modified embodiment of this invention. It is also to be noted that the described ejection of the charging plug disconnects internally within the fuse structure all connections from the charging receptacle contacts to the circuits of the fuse, thus preventing rain or moisture which may accumulate on the external contact surfaces, necessarily exposed after ejection of the charging plug, from electrically affecting operation of the fuse in any manner.

A so-called shipping wire and tag H5 attached thereto are provided as an additional safety feature by threading wire 9a through the plunger and bushings 92, I33 as well as through stop and bracket It, 89. This shipping wire would be removed after insertion of the arming wire at the time the bomb or flare is loaded into the aircraft.

The remaining components of the fuse and its mechanism are housed in the lower portion of the cylindrical fuse body II'I. Casing I24 encloses the several electrostatic condensers such as C1, C2 and C3 of Figs. 6 and 13, and elements I I 4 and I25 comprise a suitable gaseous discharge tube and its socket. As previously indicated, the requirements for a gaseous discharge tube suitable for use in connection with aircraft bombs and flares are not so exacting as those required. for use in high velocity shells and therefore the relay tube Iii may be of a type commercially available, although the tube illustrated in Figs. 3 and 4 is admirably suited for the purpose. A suitable detonating ignition device I23 is secured to adaptor I25 and .projects into the powder booster cup I22 which screws into adaptor I20. These portions of the fuse may be understood to be similar to corresponding components heretofore employed in connection with aircraft bombs and flares.

Fig. 10 shows a modification of the ejector and switching device shown in Figs. 8 and 9. Here the charging plug NH is retained against the force of spring-actuated ejection pins I 36 and I31 (there being as many as required) by the restraining action of arming wire 9| which Passes through bushing I32 and through plug IIII. With the elements in the relative positions illustrated, pins I36 and I3! not only make electrical contact at the points I43 and I44 respectively of the plug, but also make contact at their other ends with contact leaves I34 and I35. These contact leaves are connected respectively to wires 97 and 98 which it is to be understood connect with the circuits of the fuse as described in respect to Figs. 8 and 9.

Upon withdrawal of arming wire 9|, pin I36 and I 31 are forced to move by springs I48 and M8 which press on the stops I40, I4I secured to those pins. This movement will take place toward the left, in the drawings, through guide holes in insulating plates I33 and I42. The resulting pressure on the charging plug through the contacts I43 and I44 ejects the plug and simultaneously moves pins I36 and I3! out of contact with leaves I34, I 35. These pins thus perform both of the operations of ejection and switching.

In Figs. 11 and 12 a further modification is illustrated in which a retaining ring I46 secured to charging plug HM and having ears, as shown, is arranged to cooperate with brackets I48 and I 59 shaped to conform with the contour of the plug and ring, thus functionall replacing arming wire ill of Fig. 10 in locking plug IOI in position until the time of release. Otherwise the combined ejection and switching, mechanism of Fig, 11 may be understood to be similar to that of Fig. 10. These retaining brackets I48 and I49,

17 in their cooperation with the ears of retaining ring I46, are positioned on the fuse body II! in such manner that when the fuse body, as stored in the aircraft, is dropped or released therefrom, the movement of the fuse body will be in a direction such as to permit the separation of the fuse body from the charging plug in the manner illustrated in Fig. 12 where the arrow below the drawing represents the direction of movement of the fuse body with respect to the plug IIII which remains attached to cable I02. Since in the arrangement of Figs. 11 and 12 the separation'of the fuse from the contacts of the receptacle with which it is adapted to make connection, is by a sliding motion it is evident that the form of the contact will differ from that of the contacts in Fig. 8, for example, where the contacts of the plug are actuall inserted into corresponding receptacle contacts. It will be evident from the foregoing that any form of receptacle and cooperating plug may be employed so long as it be functionally suited to the purpose.

If it be desired to combine the chargin cable release arrangement of Figs, 11 and 12 witha switching device controlled by an arming wire, the structure shown in association with springactuated plunger switch I80 in Fig. 11 may be used. In thi arrangement the arming wire 91' retains spring-actuated switch plunger II-within the bushing I52 by reason of the fact'that'the wire is threaded through holes in the bushingand in the plunger. Upon withdrawal of the arming wire, switch I80 is actuated by the sprin within it to effect any necessary switching operation, and may be understood to perform any of the switching operations which are performed by the switches described in Figs. 8, 9 and 10, forexample. The shipping wire 90 is included forthe reason mentioned in connection with Fig. 8.

The system of Fig. 13 represents the preferred embodiment of my invention, and includes a time fuse and setting apparatus therefor, both especially useful in connection with aircraft bombs and flares, The circuit arrangement of the time fuse of Fig. 13 is essentially the same as that of Fig. 6, most of the differences being in the fusesetting apparatus, the connections between that apparatus and the fuse, and the incorporated switching arrangements. With this fusesetting apparatus it is possible for the bombardier or operator of the device first to select the range in which the desired time appears and then quickly to set another indicator to the exact second of that range. Then by throwing a, charging con trol, the fuses at that time connected to the apparatus will immediatel be charged to efiect detonation at the expiration of the desired number of seconds following release from the aircraft. This apparatus of Fig. 13 also includes mechanism by which before the fuses are set the potential supply may be checked, and adjusted if necessary, to make certain that the desired fuse setting will be accurate.

The system of Fig. 13 will be seen to be generally similar to the system of Fig, 6 and to include certain features of Fig. 1, but as will become'evident it includes many advantages in addition to those mentioned in connection with Figs. 1 and 6.

In this system as illustrated, five potentialselect therangedesired. a Poles Ss and S10 of this switch are connecte'd"to introduce an adjustable potentiometerresistor R3 series with the bleeder; resistors in such a way thatthe ratios of re- SiStOrfBB'tO theselected values. of the. first bank ofbleeder resistorsRn to R18 and the second bank of bleeder resistorsRr to Rzg will cause potentiolmeteriRg -tofprovide successive "and predetermined rangesof potentia1. r I

However, since the total-lvalu'e. of resistor R3 maynot beiconveniently-changed and since it is requiredio subtend different potentials it -follows that the total bleeder resistance for 'difiier ent range s will change. This change inloadjis v highly-undesirable:where great constancy. in the setting voltage- Fig-desired, and consequently by means of switch- -pole S12 a different parallel compensatingresistor is introducedfor each setting; of the switches S9 and S10. These-parallel compensatingfresistors R29 to Rs: should be chosenso that-thetotalparalleL resistance load remains A constant. .-Noactual values of-these esistpf r her ren b a se' h rmar as i ema o 5k ll n t e a o e. t e'cir' I cuit c onditions and other constants are selected.

For example, if the potential source happened to be of about the value re quiredfor thelfirstrange the first resistor in the bankmight be of a very low resistance-value, or even of zero Valuer;

A bleeder resistance connected across the direct-current source and divided into sections;

designated R2 and Rzsfinclusive, is associated with switch S11 soa s to provideselection of a number of predetermined polarizing potentials for the timing circuit of the fuse. The-advan-j tage of using'these polarizing potentials will be described in more detail in connection with Fig.

14; The's'ource of direct currentfromwhichthe necessary potentials are derived is here rep-' resented as a battery 69', andthis source is protected by safety fuses I64and I65 as well as by an on-ofi switch S13. e In order to maintain the output potentialsof the current source within exceedinglyclose limits without the use of metering equipment either too delicate or too heavy for general aircraft use,

a potential-regulating system including two-electrode gaseous discharge tubeQT1 a milliammeter I63 and'rheostat R12 maybe employedv and connecte'd, as shown". ,In this reg latingisystem ad-' vantage is taken of the'very fiat slope which the current-voltage characteristic of gaseous discharge tubes display within: certainranges; On

the basis of this phenomenon the difference of 'a' fraction of a volt in several hundred across the two electrodes of the tube will correspond to a change in currentthrough such a discharge tube of sufficient'magnitude to be easily' observed on an insensitive short scale meter suitable for use in aircraft. For this'reason it is possible to ad'- just the potential efiective across the entire po-.

put of the fusesetting apparatus through the charging cable harness to the fuses;themselves. v

When this knob (58 is thrown to the inert position the three potential-carrying wires of the main charging cable are shortcircuited and grounded. This feature of the invention operates as "a safety device to prevent accidental charging of the timing circuits of the fuses which happen then to beconnected to the charging harness, and not only thus prevents accidental operation of the fuse circuits, but also assures hat when the fusesetting operation is commenced the condensers in the fuse circuits will receive their preselected charges when in a completely discharged condition:

This armed'-inert control is also especially valuable-in aircraft operation during warfare because its use enables the bombardier instantly to discharge all the timing circuits in the bomb f'u'se ls aboard his aircraft, so that in an emergency the bombs may be jettisoned over friendly territory without being detonated. The connections, below the double dash-dot lines, to the duplicate but unlettered terminals beneath terminals E2 to En are intended to represent all the parallel branches of the charging harness connecting to all of the time fuses and bombs stored in the-aircraft. To simplify the drawings the duplicate fuses are'not shown.

As shown in the drawings, selector switches S9 and S10, whichin this instance make available five different potential and corresponding time ranges are interconnectedin uni-control arrangement by shaft I61 rotatable by the range selector knob I62. This knob is, as shown, arranged with an index to indicate the five different time ranges from A to E inclusive. On this same shaft IBI is arranged the pole of switch S11 which connects to the various sections R24R2s of the bleeder resistance above referred to from which are derived the polarizing potentials, which may be applied to a condenser in the timing circuit of the fuze in order to extend the total timing range possible with a given value of condenser capacity. Switch S12, also connected to the same shaft 6! so as to operate simultaneously with the other switches, connects with the same number of contact points as do the other four switches just referred to. The bank of resistors Rae-$2.33 there shown as connected respectively to the different points of this switch and connected in common to the positive terminal of the potential supply system is introduced as a compensator in order to keep the load on the potential supply source constant under the varying conditions of load incident to selection of the different points on the range selector. The compensating resistors R29 R33 therefore must be chosen with this purpose in mind and the resistance values thereof required under any particular circuit conditions may be calculated by one skilled in the art.

Arrows [IQ-H3 inclusive near the bottom of Fig. 13 represent the pins or connectors of a charging plug, and blocks 91-100 inclusive represent the corresponding contacts on the fuse. It will be noted that these charging plug contact pins, together with the corresponding contacts and the switch elements l26-|29 and NHL-I01 and 4.8 correspond to the elements similarly designated in the assembly shown in Figs. 8 and 9. Prior to release of the fuse and to ejection or disconnection of the charging plug therefrom the circuit is that of the configuration shown in solid lines in the drawing. However, on withdrawal of the arming wire 9! either switch plate 95 (Fig. 8) or its equivalent switch plunger I51 (Fig. 11) moves the switch poles l26l29 into the positions shown in dotted lines in Fig. 13. In other words the solid line connections indicate the charging arrangement of the fuse circuits and the dotted line connections indicate the discharge or timing operation connections effected after separation of the fuse from the charging harness, assuming the use of a fuse constructed as in Figs. 8 and 9.

As has been described in connection with Figs, 1 and 6 the timing interval is a function of the adjustable potential E1, and since precautions-have been taken by means of tube T1, rheostat R-rz and meter ifi3 to regulate the effective potentialLirnpressed on the charging circuit' of the setting apparatus, it is possible to calibrate directly in seconds the dial associated with dial pointer IE6 at the top of Fig. 13, in terms of several ranges of time. This dial pointer which controls the slider of potentiometer Ra corresponds in general to the meter pointer 61 of/Fig. 6, and it maybe moved by any convenient means such'as' knob I51.

The operation of the'fuse and setting appare tus therefor of Fig. 13 is as follows: Inthe fuse circuits of this system not only are timing condenser C1 and ignition condenser Ca initially charged, but timing condenser C2 is also given an initial polarizing charge predetermined for the given range of timing involved, sothatdt will either decrease or increase the amount of charge necessary to be transferred from condenser; C1 through resistor R1 before the potential across condenser C2 is adequate to trigger offthe relay tube 1. This polarization of the condenser C2 in which a charge is built up to the discharge or relay point, may be either positive or, negative with respect to the common potential terminal 107 of C1 and C2. In either case however itkmust not exceed thev ignition, voltage of the tube T1. between G and KY thereof if the tube, is to. be prevented from discharging prematurely. .The, values of the mentioned circuit. elements. maybe.

the same as those given the description of. Figs. 1 and 6.

The timing operation is initiated when switch pole I28 completes thetransfer path between con-. densers C1 and C2 by. connecting with contact. point 48 at the instant of .release of the fuse.- Subsequently, and when the safety air vane switch- S14 (comprising contact elements 83,05, and 86 of Fig. 8) has closed, adequate chargewill be added tothe polarizing-charge in condenser C2, whether that polarizingcharge be negative or positive, to'cumulatively ionize the discharge-path G--K of relay tube I, This will initiate the relay action in tube 1 and release the energy of ignitioncondenser C3 to ignite detonator' 44; The action of the limiting resistor R2 is the same as in the circuit illustrated in Fig.6, and its-value maylikewise be 10,000 ohms.

By reference'to the curves of Fig. 14 the effect of the several different polarizing voltages (po tentials) employed to charge condenser C2 may be seen; as well as' the relation between the charging voltage E1 of condenser C1 aiod'the re'-' sulting timing of the fuse. These voltages are'similar to the voltages which would be produced by measuring 'the time-voltage. fuse characteristics fora series of discharge tubes having progressively higher ignition potentials. The ive voltage and time ranges marked AE Fig.13 are here represented by the same letters These five curves show the rangesin seconds which were se-' cured with thecircuit as shown inFigI when employing elements a described in connection therewith, with two difierent variables. The first variable is the different polarizing voltages E3 and the second is the different charging or timing voltages E1 represented by the ordinates on the graph. As pointed out in connection with Fig. 13 the selector of the different polarizing potentials results from moving switch II, and the selection of the different potential ranges is effected by switches S9 and S10, whereas the fine selection of potential within each range is effected by potentiometer R3. The different polarizing potentials are applied to timing condensers C2 and charge the same to those potentials. The voltage range indicated on each curve by the vertical line is the voltage simultaneously applied to timing condenser C1. All of the voltages, r potentials, represented in Fig. 14 were employed successfully in connection with a discharge tube as represented in Figs. 3, 4 and 8.

The consequence of the series of progressive polarizations shown in Fig. 14: is to permit a substantially wider range of time intervals to be covered with a single set of component circuit values and also improved accuracy throughout all of the ranges due to the steeper slope of the curve obtained by subdivision of the total possible time range into a group of appropriately polarized ranges.

It has already been explained that the electric time fuses and setting apparatus therefore above described were designed for use especially with aircraft bombs and flares and high velocity shells. However, it will be evident to those skilled in the art that the several features of my invention will have a wide range of applicability wherever timing circuits, or ignition circuits are required, or wherever charging apparatus or electrical fusesetting apparatus is employed.

I claim:

1. In an electrical time fuse, the combination of a timing circuit, an ignition circuit and a gaseous discharge tube having a discharge path connected effectively in common to said circuits, said timing circuit including a first timing condenser connected to receive a timing charge, a second timing condenser connected to receive a polarizing charge, and a timing resistance connectable between said condensers, said ignition circuit including an ignition condenser connected to receive an ignition charge which is independent of the charges in said first and second condensers, and an ignition element connected to receive ignition energy from said ignition condenser.

2. In an electrical time fuse, the combination of three condensers, an ignition element and a plurality of coupling means, connections for coupling two of said condensers by one of said coupling means in a timing circuit whereby said con-- densers are connected to receive separate electrical charges, coupling means connected between one of said two condensers and an ignition circuit, said ignition circuit including the third condenser and said ignition element, and means for connecting said third condenser to receive an electrical charge independent of the charges in said two condensers.

3. In an electrical time fuse, the combination of three condensers, an ignition element, a resistance and a three-electrode gaseous discharge tube, connections for coupling two of said condensers by said resistance, one of said two condensers being connected to two electrodes of said tube, an ignition circuit including said ignition element, the third condenser, one of aid two electrodes and the third electrode of said tube,

22 and meals for introducingseparate electrical charges simultaneously in all three condensers.

4. In an electrical time fuse, the combination which comprises a timing circuit includingtwo capacitors and at least one resistor, a separate ignition circuit including a third capacitor and an ignition element, a gaseous discharge tube havingthree electrodes and adischarge-path'be I, tween the first and second of said electrodes, the

third electrode being electrically associated with said path, connections including said first andsecond electrodes in series in said ignition'circuit and connections between said first and third electrodes and said timing circuit.

5. In an electrical time fuse the combination which comprises a gaseous discharge tub including three electrodes, a limiting resistance, a timing circuit including a timing resistanc and two condensers connected on one side each to a common terminal and to a first electrode of said tube, and connected on the other side through said timing resistance to each other, one terminal of said timing resistance being connected through said limiting resistance to a second electrode of said tube, an ignition circuitincluding an ignition element and an ignition condenser,

said ignition condenser being connected on one side to said common terminal and being connected on the other side through said ignition element to a third electrode of said tube.

6. In an electrical time fuse, the combination which comprises a gaseous discharge tube including three electrodes, a limiting resistance, a timing circuit including a timing resistance and two condensers connected on one side each to a common charging terminal and to a first electrode of said tube and connected on the other side through said timing resistance to each other, said timing resistance having two terminals, one terminal of said timing resistance being connected through said limiting resistance to a second electrode of said tube, said limiting resistance having a greatly lower value than that of said timing resistance, and the other terminal of said timing resistance being connected to a second charging terminal, and an ignition circuit including an ignition element and an ignition I condenser, said ignition condenser being connected on one side to said common charging terminal and being connected on the other side through saliod ignition element to a third electrode of said tu e.

7. In an electronic time fuse, the combination which comprises, a gaseous discharge tube including a cathode, an anode and a control electrode, a discharge path within said tub between said cathode and anode, a timing circuit including a timing condenser and a timing resistance connected between said cathode and control electrode, an ignition circuit including an ignition condenser and a detonating device connected in series between said cathode and anode, and connections through which said condensers may be charged, said timing and ignition circuits being electrically isolated from each other except through said discharge path within th tube.

8. In an electronic time fuse, the combination which comprises, a gaseous discharge device including three electrodes, a discharge path within said device associated with said electrodes, a timing circuit including as elements a timing condenser and a timing resistance connected to a first and a second of said electrodes, an ignition circuit including as elements a detonator and an ignition condenser connected to said third 23 electrode and to one of' said first two electrodes, and connections through which saidcondensers maybe charged, said timing and ignition circuits being electrically isolated from each other except through said discharge path within the tube.

9. In an electronic time fuse, the combination which comprises, a gaseous discharge device including three electrodes, a discharge path within said device associated with said electrodes, a timing circuit including as elements a timing resistance and a timing condenser effectively connected between a first and a second of said elec- 24 trodes, an ignition circuit. including as elements a detonator and an ignition condenser effectively connected between said third electrode and one of said first two electrodes, said timing condenser being of accurate low loss type and said ignition condenser having a capacity value much greater than that of said timing condenser, and connections throughwhich said condensers may be charged, said timing and ignition circuits being electrically isolated from each other except through said discharge path.

NATHANIEL B. WALES, JR.

Certificate of Correction Patent No. 2,404,553. July 23, 1946. NATHANIEL B. WALES, JR.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 5, line 65, for fixed read fired; column 8, line 11, before stages insert last; column 13, line 8, for fhom read from; column 19, line 40, for fuze read fuse; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 15th day of October, A. D. 1946.

LESLIE FRAZER.

First Assistant Commissioner of Patents.

Certificate of Correction Patent No. 2,404,553. July 23, 1946. NATHANIEL B. WALES, JR.

It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 5, line 65, for fixed read fired; column 8, line 11, before stages insert last; column 13, line 8, for fhom read from; column 19, line 40, for ffuze read fuse; and that the said Letters Patent should be read with these correctlons therein that the same may conform to the record of the case in the Patent Oflice.

Signed and sealed this 15th day of October, A. D. 1946.

LESLIE FRAZER.

First Assistant Commissioner of Patents. 

